Systems and methods for generating an inspection image of an object from radiographic imaging

ABSTRACT

There is described a method for forming an inspection image of an object from radiographic imaging. The method has: forming the inspection image including scaling a feature of the object in one or more digital images to a common scale, the digital images including first and second digital images of the object, the first digital image having the feature at a first scale, the first digital image having a first grain diffraction pattern at the first scale, the second digital image having the feature at a second scale different from the first scale, the second digital image having a second grain diffraction pattern at the second scale, the second grain diffraction pattern different from the first grain diffraction pattern, the common scale common to both the first and second digital images after said scaling, and removing grain differences between the first and second grain diffraction patterns at the common scale.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent application no.17/724,581 filed on Apr. 20, 2022, the entire contents of which arehereby incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to radiographic imaging, andmore particularly to imaging of objects under inspection usingindustrial radiography to perform non-destructive testing.

BACKGROUND OF THE ART

Non-destructive testing (NDT) refers to various techniques used toevaluate the properties of a material, component, or system withoutcausing damage. Such techniques may also be referred to asnon-destructive examination (NDE), non-destructive inspection (NDI), andnon-destructive evaluation (NDE). Industrial radiography is a modalityof NDE that uses ionizing radiation to inspect objects in order tolocate and quantify defects and degradation in material properties thatwould lead to the failure of engineering structures.

While existing systems for industrial radiography are suitable for theirpurposes, improvements remain desirable.

SUMMARY

In accordance with a broad aspect, there is provided a method forforming an inspection image of an object from radiographic imaging, themethod comprising: forming the inspection image including scaling afeature of the object in one or more of a plurality of digital images toa common scale, the plurality of digital images including at least afirst digital image of the object and a second digital image of theobject, the first digital image having the feature of the object at afirst scale, the first digital image having a first grain diffractionpattern at the first scale, the second digital image having the featureof the object at a second scale, the second digital image having asecond grain diffraction pattern at the second scale, the second scalebeing different from the first scale, the second grain diffractionpattern being different from the first grain diffraction pattern, thecommon scale being common to both the first digital image and the seconddigital image after said scaling, and removing grain differences betweenthe first grain diffraction pattern and the second grain diffractionpattern at the common scale.

In accordance with another broad aspect, there is provided a system forforming an inspection image of an object from radiographic imaging, thesystem comprising: a processing unit; and a non-transitorycomputer-readable medium having stored thereon program instructionsexecutable by the processing unit for: forming the inspection imageincluding scaling a feature of the object in one or more of a pluralityof digital images to a common scale, the plurality of digital imagesincluding at least a first digital image of the object and a seconddigital image of the object, the first digital image having the featureof the object at a first scale, the first digital image having a firstgrain diffraction pattern at the first scale, the second digital imagehaving the feature of the object at a second scale, the second digitalimage having a second grain diffraction pattern at the second scale, thesecond scale being different from the first scale, the second graindiffraction pattern being different from the first grain diffractionpattern, the common scale being common to both the first digital imageand the second digital image after said scaling, and removing graindifferences between the first grain diffraction pattern and the secondgrain diffraction pattern at the common scale.

In accordance with yet another broad aspect, there is provided a methodfor inspecting an object from radiographic imaging, the methodcomprising: scaling a feature of the object in one or more of aplurality of digital images to a common scale, the plurality of digitalimages including at least a first digital image of the object and asecond digital image of the object, the first digital image having thefeature of the object at a first scale, the first digital image having afirst grain diffraction pattern at the first scale, the second digitalimage having the feature of the object at a second scale, the seconddigital image having a second grain diffraction pattern at the secondscale, the second scale being different from the first scale, the secondgrain diffraction pattern being different from the first graindiffraction pattern, the common scale being common to both the firstdigital image and the second digital image after said scaling; formingan inspection image from the feature of the object common to the digitalimages at the common scale, and without grain differences between thefirst grain diffraction pattern and the second grain diffraction patternat the common scale; and inspecting the object using the inspectionimage.

Features of the systems, devices, and methods described herein may beused in various combinations, in accordance with the embodimentsdescribed herein. More particularly, any of the above features may beused together, in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1A is an example of a digital image of an object taken at a firstobject-detector and object-source position;

FIG. 1B is an example of a digital image of an object taken at a secondobject-detector and/or object-source position;

FIG. 1C is an example of an inspection image generated from the digitalimages of FIGS. 1A and 1B;

FIG. 2A is a schematic diagram of an example industrial radiographysystem with a displaceable object located at a first position;

FIG. 2B is a schematic diagram of an example the industrial radiographysystem of FIG. 2A with the object located at a second position;

FIG. 2C is a schematic diagram of another example radiography system forwith a displaceable object located at a third position;

FIG. 3A is a schematic diagram of an example industrial radiographysystem with a displaceable detector;

FIG. 3B is a schematic diagram of an example industrial radiographysystem with a displaceable source;

FIG. 4 is a block diagram of an example computing device for generatingan inspection image;

FIG. 5 is a flowchart of a method for generating an inspection image;and

FIG. 6 is a flowchart of a method for inspecting an object.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION

An industrial radiography system can be used for performingnon-destructive testing (NDT) on metal-based objects for evaluation ofdiscontinuities and/or defects/flaws within material volume. Objects fortesting are generally produced through common manufacturing processessuch as welding, casting, additive or composite aero-structures. Forexample, the object can be an aircraft component, such as a heavy alloycast airfoil or a light alloy cast accessory gearbox. Radiographicinspection, when applied to objects produced with these processes, mayinherently produce patterns on radiographs due to a diffraction effect,also known as mottle, caused by the preferential diffraction of photonstravelling through the grain structure of the object material. Thesepatterns can obscure relevant indications or defects on the finalradiograph of the object for inspection, such as common process-relateddefects within the object. Grain diffraction can contribute to addedinspection times, false positives, or false negatives where defects havepotential to be missed.

There is described herein systems and methods for generating inspectionimages of objects through radiographic imaging, where the effect ofgrain diffraction is reduced and/or eliminated. Referring to FIG. 1A,there is illustrated an example of a first digital image I₁ of anobject. A defect 100 is obstructed by a first grain diffraction pattern102. Image I₁, was taken with the object positioned between a radiationsource and a photon beam detector, at a first object-detector distanced_(od_1) and a first object-source distance d_(os_1). The graindiffraction pattern 102 is caused by photon beams emitted by theradiation source impinging on the object at a given incident angle.

Referring to FIG. 1B, there is illustrated an example of a seconddigital image I₂ of the same object, where at least one of theobject-detector distance and the object-source distance has changed. Thedefect 100 is still present and is obstructed by a new grain diffractionpattern 104. Indeed, the change in at least one of the object-detectordistance and the object-source distance causes the grain diffractionpattern in the digital image to change due to a change in the incidentangle of the photon beams on the object, thus leading to a unique graindiffraction pattern per relative position of the object with respect tothe source and the detector.

An inspection image is formed from digital images I₁ and I₂. Morespecifically, only the image features found in both digital images I₁and I₂, i.e. that are common to both digital images, are retained andthe unique diffraction patterns are removed in order to form theinspection image I_(insp), an example of which is illustrated in FIG.1C. It will be understood that in some cases, there may be remnants ofthe diffraction patterns in the inspection image I_(insp). However, theinspection image will have significantly less noise, thus facilitatinginspection. Although the examples herein show the inspection imageI_(insp) generated from two images, it will be understood that more thantwo images may be used. Visual inspection and/or assisted defectrecognition systems may be used to inspect the object using theinspection image I_(insp.)

Referring to FIG. 2A, there is illustrated an example industrialradiography system 200 for acquiring digital images of an object 202that can be used to generate an inspection image. As used herein, theexpression “digital image” refers to a digital radiograph obtainedthrough radiographic imaging with the object at a fixed position. Adigital image may be obtained from a single radiographic exposure of theobject at the fixed position to ionizing or non-ionizing radiation, orfrom multiple radiographic exposures of the object 202 at the fixedposition. Any known techniques for combining multiple radiographicexposures of the object at the fixed position may be used to obtain thedigital image. For example, frame averaging may be used to reduce noisepatterns created by factors such as scattering. Other image processingtechniques may also be used.

In some embodiments, the industrial radiography system 200 is a digitalradiography (DR) system. The object 202 is positioned between the source204 and the detector 206 for imaging thereof. The source 204 is an X-raygenerator having components arranged therein to generate high-energyelectromagnetic radiation in the form of X-rays. Alternatively, thesource 204 is a gamma ray generator that generates gamma rays by thenatural radioactivity of sealed radionuclide sources. Other types ofradiation may also be used. The source 204 produces photon beams 208_(i), that are projected towards the object and captured by the detector206. Although only four photon beams 208 _(i), are illustrated, more orless beams may be projected onto the object 202. For illustrationpurposes, beams 208 ₂ and 208 ₃ are shown intersecting the object 202and beams 208 ₁ and 208 ₄ are shown not intersecting the object 202.

The detector 206 is a digital image capture device that captures thebeams 208 _(i), as they impinge on a surface 210 thereof. In someembodiments, the digital image capture device is an indirect flat paneldetector, where the photon beams are converted to light and the light isconverted to charge. In some embodiments, the digital image capturedevice is a charge-coupled device (CCD) detector, where the photon beamsare converted to light and the light is converted to charge. In someembodiments, the digital image capture device is a direct flat paneldetector, where the photon beams are converted directly into charge. Thecharge may be read out using a thin film transistor array to form adigital image.

In some embodiments, the industrial radiography system 200 includes asystem controller 230 operatively connected to the source 204, thedetector 206, or both, through wired and/or wireless connections 232.For example, the connections 232 can include co-axial cable(s), Wi-Fi,infrared, Zigbee, Bluetooth, optical fibers, and any other communicationtechnology for exchanging data between the system controller 230 andother components of the system 200. The system controller 230 iscomposed of software and hardware components arranged to control thesystem 200 by triggering the source 204 and/or operating the detector206. The captured photon beams 208 _(i), may be converted to light bythe system controller 230. The captured photon beams 208 _(i), may alsobe converted to charges by the system controller 230. The systemcontroller 230 can read out the charge so as to form an image. In someembodiments, the system controller 230 performs image processing on theacquired images, as will be explained in more detail below.

In some embodiments, the industrial radiography system 200 is a computedradiography (CR) system. In this case, the detector 206 is acassette-based phosphor storage plate which is then scanned into adigital format to produce the digital image.

In order to obtain the first image I₁,the object 202 is positioned at afirst location between the source 204 and the detector 206. When theobject is at the first location, the object 202 and detector 206 areseparated by an object-detector distance of d_(od_1), and the object 202and source 204 are separated by an object-source distance of d_(os_1),where the sum of the object-detector distance and the object-sourcedistance is a source detector distance d_(sd_1). Photon beams 208 ₂, 208₃ impinge on the object at a given angle of incidence, contributing tothe grain diffraction pattern 102 as illustrated in FIG. 1A. Forexample, photon beam 208 ₂ has an incident angle θ₁ on the object 202.

In some embodiments, the object-detector distance and/or object-sourcedistance is changed by displacing the object 202 while the source 204and the detector 206 remain fixed. For example, the object 202 may befixedly mounted to a support 212 attached to a base 214. The base 214translates the object 202 along a Z-axis, for example via a track 216,to position the object 202 at a second location, in order to obtain thesecond image I₂. In some embodiments, translation of the object 202 iseffected by the system controller 230, which can be operativelyconnected to the support 212, base 214, track 216, or any combinationthereof.

FIG. 2B illustrates an example where the object 202 has been translatedalong the track 216 to the second location. Translation of the objectleads to a new object-detector distance d_(od_2), whered_(od_2)<d_(od_1), and a new object-source distance d_(os_2), whered_(os_2)<d_(os_1). Note that the source-detector distance d_(sd_1) hasnot changed as the source 204 and detector 206 remain fixed while theobject 202 is displaced. In this example, photon beam 208 ₂ has anincident angle θ₂ ‡ θ₁ on the object 202, thus causing a different graindiffraction pattern 204 in image I_(2.)

FIG. 2C illustrates an alternative embodiment for translating the object202 to a new location along the Z-axis. In this example, the track 216is omitted, the base 214 extends along the Z-axis, and the support 212translates along the base 214. The object 202 is thus located atlocation Z₃, which leads to a new object-detector distance d_(od_3),where d_(od_2)<d_(od_1)<d_(od_3), and a new object-source distanced_(os_3), where d_(os_2)>d_(os_1), >d_(os_3). Again, the source-detectordistance d_(sd_1) has not changed as the source 204 and detector 206remain fixed while the object 202 is displaced. A new incident angle θ₃results from the beam 208 ₂ impinging on the object 202, thus againchanging the grain diffraction pattern in a digital image acquired withthe object at this new location.

In some embodiments, the object 202 remains fixed and it is the source204 or the detector 202 that translates along the Z-axis. Examples areshown in FIGS. 3A and 3B. In FIG. 3A, the detector 206 is mounted to asupport 302 that translates along a base 304 along the Z-axis. In thiscase, the object-detector distance varies (d_(od_4)) while theobject-source distance remains fixed (d_(os_3)). The source-detectordistance (d_(sd_2)) changes for each image acquisition. In FIG. 3B, thesource 204 is mounted to the support 302 that translates along the base304 along the Z-axis. This configuration allows the object-sourcedistance (d_(os_3)) to be varied between image acquisitions while theobject-detector distance (d_(od_3)) remains fixed. The source-detectordistance (d_(sd_1)) changes for each image acquisition. It will beunderstood that when the object-source distance changes, certainrequirements may be imposed to ensure a suitable sharpness for the imageand a desired resolution, and to avoid an excessive penumbral effect.For example, there may be a minimum value for the object-sourcedistance. Other constraints may also apply.

In some embodiments, the inspection image can be generated using acomputing device 400 as illustrated in FIG. 4 . It should be noted thatthe computing device 400 may be implemented as part of the systemcontroller 230 or separately therefrom. Indeed, the computing device 400can form part or all of the system controller 230. In some embodiments,the computing device 400 is within the system controller 230 andcooperates with other hardware and/or software components therein. Insuch cases, the system controller 230 generates the inspection image. Insome embodiments, the computing device 400 is external to the systemcontroller 230 and interacts with the system controller 230, for exampleto obtain the digital images and/or to transmit parameters for acquiringthe digital images. In some embodiments, some hardware and/or softwarecomponents are shared between the system controller 230 and thecomputing device 400, without the computing device 400 being integral tothe system controller 230. In this case, the system controller 230 canperform part of the steps for generating the inspection image.

The computing device 400 comprises a processing unit 402 and a memory404 which has stored therein computer-executable instructions 406. Theprocessing unit 402 may comprise any suitable devices configured tocause a series of steps to be performed such that instructions 406, whenexecuted by the computing device 400 or other programmable apparatus,may cause functions/acts/steps described herein to be executed. Theprocessing unit 402 may comprise, for example, any type ofgeneral-purpose microprocessor or microcontroller, a digital signalprocessing (DSP) processor, a CPU, an integrated circuit, a fieldprogrammable gate array (FPGA), a reconfigurable processor, othersuitably programmed or programmable logic circuits, or any combinationthereof.

The memory 404 may comprise any suitable known or other machine-readablestorage medium. The memory 404 may comprise non-transitory computerreadable storage medium, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Thememory 404 may include a suitable combination of any type of computermemory that is located either internally or externally to device, forexample random-access memory (RAM), read-only memory (ROM),electro-optical memory, magneto-optical memory, erasable programmableread-only memory (EPROM), and electrically-erasable programmableread-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like. Memory404 may comprise any storage means (e.g., devices) suitable forretrievably storing machine-readable instructions 406 executable byprocessing unit 402.

With reference to FIG. 5A, there is illustrated an example method 500for generating the inspection image, as performed, for example, by thecomputing device 400. The steps for the method 500 may be embodied asinstructions 416 stored in memory 414 of the computing device 400.

At step 502, a plurality of digital images of the object are obtained atdifferent object-detector distances and/or object-source distances. Insome embodiments, obtaining the digital images comprises receiving thedigital images having been acquired by a separate device, such as thesystem controller 230. In some embodiments, obtaining the digital imagescomprises retrieving the digital images, for example from a database,library, or other storage medium that is local or remote to thecomputing device 400. In some embodiments, obtaining the digital imagescomprises acquiring the digital images by controlling the components ofthe industrial radiography system 200. In some embodiments, obtainingthe digital images comprises acquiring the digital images by causing thesystem controller 230 to acquire the digital images.

The different object-detector and/or object-source distances at whichthe digital images are acquired can be input manually or they can bepre-programmed and stored in the memory 414. Alternatively, theobject-detector and/or object-source distances are stored remotely tothe computing device 400 and retrieved by the computing device 400. Insome embodiments, parameters used to compute the object-detector and/orobject-source distances are pre-programmed or retrieved from a remotelocation. For example, the parameters may indicate that the initialobject-detector and/or object-source distance be increased by a fixedvalue for each digital image acquisition. In another example, theparameters may indicate that the fixed value changes between eachdigital image acquisition. In either case, the new distance can becomputed in real-time by the computing device 400 based on theparameters and on the initial position of the object with respect to thesource and the detector. The initial position of the object may bedictated by an operator of the industrial radiography system 200 uponmounting of the object, it may be pre-set, or it may be determineddynamically based on one or more parameter. In the latter two cases, thecomputing device 400 displaces the object 200 to its initial position.As indicated above, the object-detector and/or object-source distancescan be changed by displacing any one of the object, the source, and thedetector. Such displacement may, in some embodiments, be effected by thecomputing device 400 and form part of the method 500, at step 502.

When the digital images are acquired with different object-detectordistances, the digital images may need to be registered to a commonscale, as per step 503. A common scale is understood to mean that thedigital images are based on a same image coordinate system, whereby thepixels are positioned at a same location and orientation from one imageto the other. The phenomenon that results from acquiring images atdifferent object-detector distances is illustrated with FIGS. 1A and 1B,where the defect 100 is shown to be smaller in FIG. 1A than it is inFIG. 1B. Image registration refers to selecting one of the digitalimages as the designated view and registering the other digital imagesto the designated view through image processing techniques such asfeature recognition, absolute pixel binning, or interpolated pixelbinning. In some embodiments, image registration comprises scaling oneor more of the digital images. Any known techniques may be used toperform image registration. In the example of FIGS. 1A and 1B, image 1Bis registered to the view of FIG. 1A, such that the scale of FIG. 1A ismaintained for the defect 100 in FIG. 1C.

When only the object-source distance changes and the object-detectordistance remains fixed, step 503 can be omitted. Step 503 can also beomitted if the digital images are registered to the common scale priorto being obtained at step 502. For example, the digital images may beregistered by the system controller 230 and subsequently transmitted tothe computing device 400. In another example, registered digital imagesare stored on a remote storage device and retrieved by the computingdevice 400 at step 502. Other embodiments are also considered.

At step 504, the inspection image is formed from image features that arecommon to the digital images acquired with different object-detectorand/or object-source distances, and the grain diffraction patternsunique to each digital image are removed.

In some embodiments, step 504 is performed using pixel to pixelcomparison between the two or more digital images. A pixel of an outputimage is set to zero (“0”) if the corresponding pixel values of thedigital images are different, and is set to one (“1”) if thecorresponding pixel values of the digital images are the same. Thecomparison can be initially performed with two digital images as inputto obtain an output image. The comparison is then repeated with theoutput image as one of the input images and another digital image as theother input image. The process may be repeated for as many digitalimages as needed. Alternatively, the comparison may be performed in asingle step, with all of the digital images as input, in order togenerate the inspection image as the output image. This process resultsin an inspection image similar to that illustrated in FIG. 1C.

In another embodiment, step 504 can be performed using pixel subtractionfollowed by image inversion. A pixel of an output image is set as thedifference between a pixel value from a first image and a correspondingpixel value from the second image. In this manner, all common imagefeatures (i.e. same pixel values) would be set to zero and non-commonimage features (i.e. different pixel values) would result in a non-zerovalue. By inversing the zero and non-zero values from the output image,i.e. mapping the non-zero values to zero and the zero values tonon-zero, an inspection image similar to that illustrated in FIG. 1Cresults.

Many different image arithmetic techniques may be used to generate theinspection image, as will be readily understood by those skilled in theart. It will also be understood that the method 500 can be performed bythe computing device 400 in substantially real-time.

In some embodiments, the method 500 is performed a plurality of timesper object. For example, the object 202 may have up to six degrees offreedom, such that it can be translated up, down, left, and right aswell as rotated about each one of its axes. It may be desirable toobtain multiple views of the object 202, in order to increase thecoverage obtained. As such, the method 500 may be performed for eachview of the object 202. Each iteration of the method 500 results in aninspection image for a given view.

With reference to FIG. 6 , there is illustrated a method 600 forinspecting an object. In some specific and non-limiting examples, theobject is an aircraft component, such as an airfoil. In some specificand non-limiting examples, the object is an engine component, such as anaccessory gearbox. Other aircraft and/or engine components may alsoapply.

All of the embodiments described with respect to the method 500 of FIG.5 also apply to the method 600 of FIG. 6 . At step 602, the inspectionimage as generated from steps 502-504 is used to inspect the object. Theinspection may be visual, automated, or a combination thereof. In someembodiments, step 602 comprises an automated inspection performed by thecomputing device 400. Any known inspection technique based on digitalimaging may be used for step 602.

The methods and systems described herein may be implemented in a highlevel procedural or object oriented programming or scripting language,or a combination thereof, to communicate with or assist in the operationof a computer system, for example the computing device 400.Alternatively, the methods and systems described herein may beimplemented in assembly or machine language. The language may be acompiled or interpreted language.

Embodiments of the methods and systems described herein may also beconsidered to be implemented by way of a non-transitorycomputer-readable storage medium having a computer program storedthereon. The computer program may comprise computer-readableinstructions which cause a computer, or more specifically the processingunit 402 of the computing device 400, to operate in a specific andpredefined manner to perform the functions described herein.

Computer-executable instructions may be in many forms, including programmodules, executed by one or more computers or other devices. Generally,program modules include routines, programs, objects, components, datastructures, etc., that perform particular tasks or implement particularabstract data types. Typically the functionality of the program modulesmay be combined or distributed as desired in various embodiments.

The embodiments described in this document provide non-limiting examplesof possible implementations of the present technology. Upon review ofthe present disclosure, a person of ordinary skill in the art willrecognize that changes may be made to the embodiments described hereinwithout departing from the scope of the present technology. For example,the methods 500, 600 may be fully integrated into a digital radiography(DR) or computed radiography (CR) system. The DR or CR system may beencased in a housing that includes the source 204, detector 206, andsupport 212, with an embedded system controller 230 having all of thefunctions described herein for changing the object-detector and/orobject-source distance between image acquisitions and generating theinspection image from the acquired digital images. Yet furthermodifications could be implemented by a person of ordinary skill in theart in view of the present disclosure, which modifications would bewithin the scope of the present technology.

1. A method for forming an inspection image of an object fromradiographic imaging, the method comprising: forming the inspectionimage including scaling a feature of the object in one or more of aplurality of digital images to a common scale, the plurality of digitalimages including at least a first digital image of the object and asecond digital image of the object, the first digital image having thefeature of the object at a first scale, the first digital image having afirst grain diffraction pattern at the first scale, the second digitalimage having the feature of the object at a second scale, the seconddigital image having a second grain diffraction pattern at the secondscale, the second scale being different from the first scale, the secondgrain diffraction pattern being different from the first graindiffraction pattern, the common scale being common to both the firstdigital image and the second digital image after said scaling, andremoving grain differences between the first grain diffraction patternand the second grain diffraction pattern at the common scale.
 2. Themethod of claim 1, further comprising registering the digital images tothe common scale prior to said forming the inspection image.
 3. Themethod of claim 1, wherein said forming the inspection image comprisesperforming a pixel to pixel comparison between the digital images, andsetting pixels of the inspection image to zero when the pixel values ofthe digital images differ and non-zero when the pixel values of thedigital images match.
 4. The method of claim 1, further comprisingacquiring the first digital image of the object at a firstobject-detector distance, and acquiring the second digital image of theobject at a second object-detector distance different from the firstobject-detector distance.
 5. The method of claim 4, wherein saidacquiring the first digital image and said acquiring the second digitalimage comprises translating the object from a first location at thefirst object-detector distance to a second location at the secondobject-detector distance.
 6. The method of claim 4, wherein saidacquiring the first digital image and said acquiring the second digitalimage comprises translating a radiation detector from a first locationat the first object-detector distance to a second location at the secondobject-detector distance.
 7. The method of claim 1, wherein saidradiographic imaging is performed using a radiation source generatingpenetrating radiation along a radiation path extending between aradiation source and a radiation detector, the object being positionedbetween the radiation source and the radiation detector, across theradiation path, and wherein the radiation source is an x-ray generator.8. The method of claim 7, wherein the radiation detector is a digitalimage capture device, and wherein the radiation source and the radiationdetector form a digital radiography system.
 9. The method of claim 7,wherein the radiation detector is a cassette-based phosphor storageplate, and wherein the radiation source and the radiation detector forma computed radiography system.
 10. The method of claim 1, wherein theobject is an aircraft component.
 11. A system for forming an inspectionimage of an object from radiographic imaging, the system comprising: aprocessing unit; and a non-transitory computer-readable medium havingstored thereon program instructions executable by the processing unitfor: forming the inspection image including scaling a feature of theobject in one or more of a plurality of digital images to a commonscale, the plurality of digital images including at least a firstdigital image of the object and a second digital image of the object,the first digital image having the feature of the object at a firstscale, the first digital image having a first grain diffraction patternat the first scale, the second digital image having the feature of theobject at a second scale, the second digital image having a second graindiffraction pattern at the second scale, the second scale beingdifferent from the first scale, the second grain diffraction patternbeing different from the first grain diffraction pattern, the commonscale being common to both the first digital image and the seconddigital image after said scaling, and removing grain differences betweenthe first grain diffraction pattern and the second grain diffractionpattern at the common scale.
 12. The system of claim 11, wherein theprogram instructions are further executable for registering the digitalimages to the common scale prior to said forming the inspection image.13. The system of claim 11, wherein said forming the inspection imagecomprises performing a pixel to pixel comparison between the digitalimages, and setting pixels of the inspection image to zero when thepixel values of the digital images differ and non-zero when the pixelvalues of the digital images match.
 14. The system of claim 11, furthercomprising acquiring a first digital image of the object at a firstobject-detector distance, and acquiring the second digital image of theobject at a second object-detector distance different from the firstobject-detector distance.
 15. The system of claim 14, wherein saidacquiring the first digital image and said acquiring the second digitalimage comprises translating the object from a first location at thefirst object-detector distance to a second location at the secondobject-detector distance.
 16. The system of claim 14, wherein saidacquiring the first digital image and said acquiring the second digitalimage comprises translating a radiation detector from a first locationat the first object-detector distance to a second location at the secondobject-detector distance.
 17. The system of claim 11, wherein saidradiographic imaging is performed using a radiation source generatingpenetrating radiation along a radiation path extending between aradiation source and a radiation detector, the object being positionedbetween the radiation source and the radiation detector, across theradiation path, wherein the radiation source is an x-ray generator. 18.The system of claim 17, wherein the radiation detector is a digitalimage capture device, and wherein the radiation source and the radiationdetector form a digital radiography system.
 19. The system of claim 17,wherein the radiation detector is a cassette-based phosphor storageplate, and wherein the radiation source and the radiation detector forma computed radiography system.
 20. A method for inspecting an objectfrom radiographic imaging, the method comprising: scaling a feature ofthe object in one or more of a plurality of digital images to a commonscale, the plurality of digital images including at least a firstdigital image of the object and a second digital image of the object,the first digital image having the feature of the object at a firstscale, the first digital image having a first grain diffraction patternat the first scale, the second digital image having the feature of theobject at a second scale, the second digital image having a second graindiffraction pattern at the second scale, the second scale beingdifferent from the first scale, the second grain diffraction patternbeing different from the first grain diffraction pattern, the commonscale being common to both the first digital image and the seconddigital image after said scaling; forming an inspection image from thefeature of the object common to the digital images at the common scale,and without grain differences between the first grain diffractionpattern and the second grain diffraction pattern at the common scale;and inspecting the object using the inspection image.